


Thunderstruck

by Catsitta



Series: Assorted Oneshots [12]
Category: Undertale (Video Game)
Genre: Alternate Universe - Gaster Blaster (Undertale), Alternate Universe - Underfell (Undertale), Angst, Angst with a Happy Ending, Established Relationship, Fluff and Angst, Gaster Blaster Sans (Undertale), Gift Fic, Hurt/Comfort, M/M, Romance, Suggestive Themes, Swearing, Underfell Sans (Undertale), Undertale Monsters on the Surface, kustard - Freeform
Language: English
Status: Completed
Published: 2020-06-13
Updated: 2020-06-13
Packaged: 2021-03-04 00:00:04
Rating: Mature
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 2,556
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/24704182
Author URL: https://archiveofourown.org/users/Catsitta/pseuds/Catsitta
Summary: Sans is an indulgence that Red should have known better than to keep. Even free of that hellhole under the mountain, he can’t escape the past.Kustard | Gift Fic | Gaster Blaster AU
Relationships: Sans/Sans (Undertale)
Series: Assorted Oneshots [12]
Series URL: https://archiveofourown.org/series/1413808
Comments: 14
Kudos: 137





	Thunderstruck

**Author's Note:**

  * For [silverryu25](https://archiveofourown.org/users/silverryu25/gifts).



> This is a raffle prize requested by [Silverryu25](https://silverryu25.tumblr.com/), who wanted some good ol' hurt-and-comfort kustard, with some gaster blaster angst thrown in. Hope you enjoy! I had fun with this one.

“storm moving in. i can hear the wind. you gonna head home or stick around until the power goes out, dude?”

Red doesn’t move, his coccyx firmly adhered to the couch for now, one hand thrust up the back of Sans’ shirt, phalanges absently stroking each individual vertebrae. “nah, think i’ll _weather_ it out here.” The other skeleton snorted against his chest before reaching for the remote and flipping through the channels. 500 of the things and nothing to watch but the news lady with the big bazongas and shitty syfy movie reruns. Red, not one to handle boredom with any grace, decided to entertain himself and see how low he could creep his hand before he got himself chewed out. Not that he minded a little bit of teeth on bone. Especially from the monster laying against him.

Sans is an indulgence that Red knew he shouldn’t keep, but like a god-damned addict he can’t let go, he makes excuses, needs another hit of his favorite vice, to feel warm magic under his hands, on his lap, in his arms. He’s delicate and soft in ways that were almost impossible to find back in that hellhole under the mountain. No EXP, no LV, just ones across the board for stats. Sans was the kind of monster that was one bad sneeze and a trip down a flight of stairs away from Dusting. Every instinct ingrained into Red through a kill-or-be-killed culture made him want to bundle Sans up and hide him away to be his personal basking stone of unadulterated magic.

Of course, Sans wouldn’t put up with that kind of bullshit, no matter how much Red’s proverbial, primitive lizard brain demanded it. Sans wasn’t one to be coddled. Stars, he wasn’t one to be cuddled without a thousand reasons not to bail. It took months of borderline sexual harassment on Red’s part before the prickly bastard got the hint that his evil clone from an alternate timeline wanted something other than world domination. Call him a sentimental idiot, but Red would never forget the day Sans stole a cigarette Red was actively smoking, and popped it between his own teeth, taking a long drag and shrugging away Red’s comments about them sharing a second-hand kiss. 

That moment was the start of a friendship. One built on sitting on roofs and pointed avoidance of talking about the past. It wasn’t candy and rainbows for either of them. Red just happened to get the short, pointed, murdery end of the shitty luck stick. They both had nightmares. Red dealt with them by trying to frisk Sans’ bones the next day (or that night if the other skeleton happened to have ‘slept over’.) Sans didn’t deal with his. He preferred the denial approach. Closed up like a bank vault in a high budget crime drama. Red loved to unwind him, to pick and pry at his locks and walls until Sans gave in and became a tired puddle in his arms. More than once their brothers would come home to find them curled together asleep on the couch, or floor, or wherever they happened to end up.

Despite living apart, Red and Sans were nearly inseparable these days, neither quite willing to admit that maybe they wanted more from the other. What might very well be surprising to an outsider looking in was Red’s ravenous desire for commitment, and Sans’ apparent allergy to the word. But giving whatever they had a name didn’t really matter when Red had Sans, and only Sans, and the other skeleton never looked twice at anyone BUT him. 

“tibia-honest, i didn’t realize you were just plannin’ on warming your cold ass hands when you shoved them down the back of my pants,” Sans snarked, rousing Red from his dangerously trailing thoughts. An indulgence. Indulgences made you weak if you didn’t practice moderation. Made you distracted and vulnerable. Red forced his grin into a sharkish twist.

“yer have other ideas fer what to do wit my hands?”

“yeah. you taking them off my pelvis. i’m watching a movie here, don juan.”

“i don’t think that what you _juan_ -t.”

Sans rolled his eyelights and chuckled. Edge would have screeched and Papyrus would have groaned. At least someone appreciated Red’s jokes. A soft, warm someone who was looking at him far more than the tv. He’d choke before admitting it out loud, but Sans was sanctuary. A cozy place to rest his head where he knew he wouldn’t get shanked. This timeline wasn’t his own, it wasn’t home, but Red was happy to let the past die, to burn to ash, if it meant keeping whatever this was between him and his doppleganger. Screw anyone who thought it was wrong. They could fight him and lose, because he was a bastard that didn’t know how to throw down without playing dirty.

Of course, fate was a right bitch when she wanted to be.

Just as Red was getting really comfortable, the thunder began. Both of them stiffened. Monsters as a whole didn’t like lightning or thunder, as it sounded like the sky was trying to kill them all. But when the rumbles remained low and distant, they both relaxed again, and two pairs of hands started to roam. Both seeking a distraction. Their brothers were out of town for the weekend, both part of Frisk’s security detail when they were in the role of ambassador, which meant they were alone. Neither of them really handled the whole alone thing well.

Red had his teeth tracing a line on Sans’ neck when it happened. Quick and sharp like a bullwhip, but as deep and booming as a landslide, was the thunder. It deafened at the same time light blinded. Like a camera flash (or blaster fire) illuminating the whole house, every window went white and vibrated violently in the sills, and the room was cast in a snapshot of barely-there-blue. The reaction in his soul was deep and undeniable. A flashbang just like the lightning that rocked the whole damn house. He didn’t notice the lights go out, the TV dying with a sputter of discolored static. He didn’t hear Sans mutter a curse.

No. All Red heard was his own pounding soul...and then his own whine as his Universe’s final fuck you to his happiness decided to rear its ugly head. He wanted to shortcut away, to find a safe place to hide, but he was helpless against his body’s response to an unfamiliar threat. Gaster wanted to make the brothers into the perfect weapons. Literal hounds of war. It didn’t matter that their bones cracked and distorted, that their skulls were distorted beyond recognition. It didn’t matter that the transformation from monster to beast was white-hot agony, like swallowing a branding iron fresh off the forge. What mattered to the good doctor was success. Heh. Red was always a fuck up. He couldn’t even be a science experiment correctly. Because instead of an obedient hound commanded by its creator’s hand, Red had the audacity to _think_ , to maintain his consciousness. A war machine with feelings and a free will was a failure.

_He was always a failure. Failure. FAILURE._

One that even Gaster’s heavy hand couldn’t fix. 

There was a final, gruesome crack as the transformation completed, a howl escaping his chest. Pain and fear stabbed cruel knives into Red’s core. Stars, it’d taken so long to get Sans to trust him and now? Now his biggest, goddamn secret was out on display, ripped from the bowels of his memories by a single bolt of lightning. 

_He can’t leave you if he’s dead,_ whispered a voice in his skull that sounded too much like the doctor. Red could still feel it, the choke chain around his neck, the crack of bone as he throttled his new ‘weapon’ for disobedience. _He can’t tell anyone your secret if he is dust. That’s all you’re really good for, after all. It’s what you’re made to do. Kill. A mindless beast. You played normal for all these years, but you’re nothing more than. a. dog._

“hey, easy there buddy.” Red snapped his head to look down at Sans. The other skeleton laid there on the couch, eyelights large and luminous with what had to be fear. His claws curled, ripping long rents into the upholstery as he fought down the urge to flee, to hide his greatest shame. Not a monster, but a beast playing at one. And now Sans knew. He knew. HE KNEW. And he couldn’t change back, his soul pounding too hard, reacting to Red’s dread as to mean the threat remained. “that was real scary, wasn’t it? you, uh, jumped right out of your skin, which is kinda impressive on the account of neither of us having any.” He lifted a hand and laid it tentatively on Red’s foreleg, rubbing slowly, like he was trying to soothe a rabid animal 

Red was frozen. _Kill him. Kill him. KILL HIM!_ Sans’ hand was warm. A high pitched whine built in his throat and Sans flinched back, and Red knew exactly why. It sounded like their blasters before they fired. The build up of magical energy into a beam so intense that it could make a smear mark out of most foes. Sans had 1HP. And Red was a threat to him just by existing. He was a fool for thinking he could have anything good in life. He tainted everything he touched. Even his own KARMA was jacked, poisoned by the LV that left him cold. _Subject S, are you disobeying a direct order? Terminate the threat._

The whine in his throat intensified, the air reeking of ozone as the world took on a crimson cast. 

_Subject S…_

“fire!” Sans’ left eyelight flickered gold-and-cyan and he thrust his arm nearly into Red’s ribcage as he turned his soul blue, throwing Red off of him with one, jerky movement. The attack burned out in Red’s throat. He scrambled off the couch, “look, i know you’re freaked out, but uh, i know that smell anywhere. i think the lightning hit the house.” Fire? Sans was worried about a possible fire when Red had been seconds away from dusting him on the couch? How the hell was he so calm right now? “sorry pal, i’ll let you _hound_ me about it later, but uh, i gotta check on something.” Suddenly, Red was caged in bones, still pinned to the ground by blue magic. Even Red’s brother couldn’t turn someone’s soul blue without a bullet, much less keep them weighted down like this without extreme focus. Yet here was Sans, his soft, harmless, sweet indulgence...completely subduing him.

Sans lingered, those eyelights of his filled with an emotion dangerously close to pity, “i’ll be right back, and we’ll figure this out. promise.” They both hated that word. But it fell so easily from Sans’ mouth before he shortcut away, a sputter of curses erupting from the upstairs a minute later. He heard the rush of water as he turned on the bathtub, a few more curses...silence...and then, slow, creaking steps down the stairs. He had his cellphone against his skull, “mhm, yeah, small attic fire from the lightning. caught it before it caught the gas line for the water heater. mhm. yep, turned off the gas. yep. yep.” A few more words later, he pocketed the device and returned to Red, smelling of smoke.

“whelp, never realized my lab experience would be put to work dousing a house fire. heh. buuuuuut we’re gonna need new insulation and who knows how much of the electrical got fried. that’s a problem for tomorrow me.” His smile was weak, “so, uh, sorry about this? you know how to turn back? otherwise i’ll have to hide you in the shed until the firefighters come by to make sure i didn’t miss anything.”

The cage of bones fell away, as did Sans’ hold on his soul, and despite himself, Red had to admit, he did feel safe. He felt like Sans was safe. And as the irrational terror in his soul faded, his body responded. The agony was more manageable the second time around. It wasn’t until Sans helped him to his feet, clothes against bone, that Red realized that his pants and hoodie were in ripped shreds. Not exactly a classy look, but it matched his misery. This was where Sans started asking questions. Started putting distance between them. Realized that Red was not just a half-reformed murderer but a monstrosity of a monster. That he was broken and dangerous and needed to be put down. 

“you’re shivering...c’mon, let’s get you into some new clothes before you flash the neighborhood.”

“yer sayin’ i’ll traumatize the housewives?”

“you already do that for funsies,” Sans quipped. “when you’re not savin’ cats from trees.”

“that’s boss’ job.”

“sure it is, and doomfanger II totally got off the roof by herself.”

“damn straight.” The walk to Sans’ bedroom was longer in the dark, especially when his whole body ached from the aftershocks of his unwilling transformation. He wanted to collapse into a heap and sleep a month. “y’know, aint we supposed to get out of the house that had a fire in it?”

“your nonexistent lungs having issues?”

“nah.”

Sans’ hoodie was fresh from the floor and smelled strongly of ketchup, and his double had the good grace to help him change clothes like he was a kid. (Or like a lover.) Red didn’t have the energy for the usual sass as he let himself be led back downstairs and to the kitchen, where Sans grabbed bottles of their favorite condiments before guiding him to the front lawn. It was there in the grass, chugging mustard and ketchup in the pouring rain, that the firefighters found them. Red didn’t have to say a word. Sans had it handled. 

With a quip to the EMT that checked on them that the cold went right through them, Sans made sure Red didn’t have to do a thing. He just stayed leaned against him, reveling in the warmth of familiar magic. And when they were giving the okay to go back inside, Sans was right there. Steady. Stable. Strong.

“yer gonna say anything about what happened?” Red asked as they shortcut into the bathroom, wet clothes peeled away. 

“can’t exactly hide it from paps. i mean, no power or hot water is pretty telling.”

“not that...about me.”

Sans appraised him with a long, knowing look, “say what exactly? that your doc was even more of an asshole than originally established. now, you wanna ‘port us to your place or would you prefer a cold shower in the dark?”

“i fucked up the couch…”

“you really should trim your toenails more often then,” Sans deadpanned. 

“i almost hurt yer.”

“you didn’t.”

“i could have.”

“i said, you didn’t.”

“i tried to kill you.”

“you want a trophy?” Sans’ voice was all bitterness and barbs. “or maybe a membership to the club?” Red’s apologies died as Sans dropped a towel on his head. “get in line, buddy, you don’t scare me, freaky wereskeleton or not.”

Red smiled at that, “y’know, a hot shower is soundin’ better and better.” 

Maybe Sans wasn’t just an indulgence after all.


End file.
